Side band selector receiver



H. o. PETERSON 1,849,884

SIDE BAND SELECTOR RECEIVER Filed Nov. 19, 1928 HAROLD 0. PETE ESONPatented Mar. 1.5, 1.932?

UNITED STATES PATENT OFFICE HAROLD 0. PETERSON, OF RIVERIIEAD, NEW YORK,ASSIGNOR T0 RADIO CORPORA- TION OF AMERICA, A CORPORATION OF DELAWARESIDE BAND SELECTOR RECEIVER Application filed November 19, 1928. SerialNo. 320,490.

This invention relates to the reception of high frequency signals, andmore particularly to speech or speech-simulating signals transmitted ona high frequency carrier.

The reception of speech or speech-simulating signals, when transmittedon a very high frequency carrier, has proven more difficult than thereception of simple code signals transmitted on a continuous wave highfrequency carrier. This difficulty has been most strongly felt inattempting to obtain sufliciently good quality reception, at greatdistances, for rebroadcasting.

Modulation by a speech-simulating signal results in the radiation ofcarrier and side band energies, rather than energy of a singlefrequency, and' these energies, although of only slightly differentfrequency, experience different degrees of fading, so that it ispossible for the carrier to fade while the side bands do not, resultingin a beat between the side bands which is entirely different infrequency from the desired beat between either side band and thecarrier, so causing distortion. Also, the energies of slightly differentfrequency are apt to considerably relatively fluctuate in phase, so thatat times it is possible for the beat between one side band and thecarrier to be opposed in phase relative to the beat between the otherside band and the carrier, thereby destroying the signal. At anintermediate phase angle the signal will have only an intermediatevolume.

To obviate these difficulties is the primary object of my invention, andto this end I arf the effect of fading of the carrier, I may arg rangethe receiver so that it rejects one of the side bands, and utilizes theother of the side bands for obtaining the signal. To reduce It isexceedingly d'iliicult to construct lters of suiicient discrimination topermit selection between .side band and carrier frequencies which dierby only an audio frequency, when impressed on a high frequency carrier,and to overcome this difficulty I prefer to heterodyne the collectedenergy with locally generated energy to obtain energy of intermediatefrequency, and then to filter the intermediate frequency energy, inwhich the percentage difference between the side band and carrierfrequencies has been very materially increased. This refinement,however, isl optional, and is designed merely for convenience.

My invention is described more in detail in the following specificationwhich is accompanied by drawings in which Figure 1 is a schematic wiringdiagram for one form of my invention; Figure 2 is explanatory of thefilter action employed; and Figure 3 is a diagram for an alternativeform of my invention in which the local oscillator is synchronized withthe incoming energy.

Referring to Figure l there is an antenna 2, which is coupled by atransmission line 4 to a radio frequency amplifier 6. This is followedby a heterodyne detector 8, to which energy from a local oscillator 10,of relatively high frequency, is coupled, and the resulting beat energyof intermediate frequency is led to a band pass intermediate frequencyamplifier 12. This may be arranged to reject one of the side bands andto pass the other of the side bands and the car- ,rier energy, in whichcase the output from ithe amplifier 12 may be fed directly to aldetector 14, and the resulting beat between e side band and carrieremployed for transy, ation in any suitable translating device 16, hereexemplied by a monitoring speaker 16. 'Ihe main output is preferablyamplified in 1 modification, if desired the receiver may be m arrangedso as to reject most but not all of jgfrom the receiving station servingas the the carrier, as well as one of the side bands, modulating inputfor modulating the radiatand to utilize the selected portion of thecared radio frequency energy. The rebroadcast rier to help control thefrequency of the locali station is likewise provided with amonitorjoscillator which is resupplying the missing* ing speaker 56.

carrier.

Iian amplifier and fed over a land line 52 to a rebroadcasting station54, the energy As a further modification I prefer to adjust the bandpass filter 12 so as to reject the carrier as well as one side band andto select only the other side band, and then to resupply theintermediate frequency carrier from a local oscillator 18, which iscoupled to the detector 14. In this manner a considerable degree offading may be removed, because the volume of energy from the localoscillator 18 is constant.

The action of the band pass filter 12 may be better understood byreference to Figure 2. The received radio frequency might be of anysuitable value, say 20,000 kilocycles, and the local oscillator tuned tosay 20,10() kilocycles, so as to differ from the received frequency by10() kilocycles. T his frequency is indicated in Figure 2 by the dottedline 20. The amplifier 12 is given a band pass characteristic resemblingthat indicated by the curve 22 so that only the desirable range of audiofrequency is transmitted therethrough. If it is desired to cut olf onlyone side band, and not the carrier, the filter characteristic should belike that indicated by the curve 24. The details of the filter are notdescribed, for they are known in the art, and may be found in patents toG. A. Campbell, numbered 1,227,113, 1,227,114, and 1,493- 600.

If it is desired to transfer a small percentage of the carrier throughthe filter, so as to help run the oscillator 18 in synchronism, thefilter characteristic may be made like that indicated by curve 26.

For running the local oscillator synchronously a more elaboratearrangement may be used, as indicated in Figure 3, in which the antenna30 is coupled by transmission line 32 to a radio frequency amplifier 34,which is led to a heterodyne detector 36, to which a high frequencylocal oscillator 37 also is coupled. 'Ihe arrangement so far is exactlylike that shown in Figure 1. The resulting intermediate frequency energyis fed to a band pass intermediate frequency amplifier 38, which isadjusted to pass only one side band, and the amplified side band is fedto a second detector 40.

A portion of the intermediate frequency amplifier output is taken to afilter or tuned cascade amplifier l2, which is coupled to the detector86, and which is closely tuned to the intermediate carrier frequencyitself, that is, it is arranged to symmetrically reject both side bands.rIhe resulting carrier energy is fed to a local oscillator 44, which,when the received carrier is not fading, tends to follow the frequencyof the energy supplied from the filter 42. However, should the receivedcarrier fade, the oscillator still provides carrier energy at the normalcarrier frequency. The local oscillator output is supplied to thedetector 40, and the resulting beat is translated in any suitabletranslating device, here exemplified by the loud speaker 4:6.

As in the arrangement shown in Figure 1 the energy may be broadcast in arebroadcasting station 54;.

No claim is made herein to a communication system in which only a sideband is transmitted. Such a system includes means to suppress thecarrier and a side band while the modulated energy is still feeble, andthe remaining side band is amplified in a power amplifier having alinear amplification characteristic. In the present state of the artthis arrangement, While successful with long wave energy, isinapplicable to short wave energy, because so far as I am aware no poweramplifier for very short waves having a linear amplificationcharacteristic has ever been constructed. When transmitting the carrierand both side bands the carrier is first amplified, and then modulatedby the signal energy just before being radiated. No attempt to poweramplify the modulated energy has been successful, and, of course, topower amplify a side band only is equally, if not still more difficult.

Furthermore, my arrangement is intended primarily, though notexclusively, for rebroadcasting from remotely located stations, so thatin the region surrounding the original broadcast station the receiversmay be of the ordinary detector type which respond to the beat betweenthe side bands and the carrier. However, at a remotely located receivingstation which is to collect energy for rebroadcasting over a cooperanttransmitting station, the scheme here disclosed is employed, bothbecause excellent quality is desired, and also because at the greaterdistance relative fading and phase fiuctuation of the slightly differentfrequencies is greater and therefore more objectionable. Of course, thesame advantages apply to any receiver which, even though not used forrebroadcasting, is, in contradistinction to nearby broadcast receivers,located remotely from the transmitting station.

I claim:

In a signalling system the combinations of an antenna for collectingradiated signalk modulated energy; an amplifier for amplifying thecollected energy; means for heterodyning the amplifieddeneigyfg,,afilterformfiltering a side band fromtheuheterodyned.@Ilergy; anotherfilter for` filtering the heterodyning carrier from the heterodynedenergy; a local oscillator controlled by the filtered carrier; adetector for combining the filtered side band and energ generated by thelocal oscillator; and, means for electromagnetically propagating theoutput from thedetector.

HAROLD O. PETERSON.

